Your first regexp was very close. You want to match more than one alphanumeric.

$line =~ m/([a-zA-Z0-9]+)$/;
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Two other points:

• You don't need to check for spaces before the username
• Always check to make sure the match succeeded

For your second problem, you're looking for the text between two backslashes that is followed by a space:

m{\\([a-zA-Z0-9]+)\\\s}
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